1. Field of the Invention
The present invention relates to methods and apparatus employing inert gases injected into the lower level of sloping underground oil bearing formations as a driving mechanism and water injected into the upper level of the formations as a gas blocking mechanism for increasing and extending the production of oil from underground formations nearly depleted of natural gas as a driving mechanism.
2. Description of Related Art
During geologic times marine animal and vegetable remains collected in ocean basins and were covered by the accumulation of eroded sand and sediment. Over millions of years the organic matter in those saltwater basins changed to what would become oil and gas. The weight of the layers of material that accumulated on top of the sand beds and the high density of the saltwater caused a high pressure to form in the oil and gas basins. Seawater flowing in subterranean strata and other natural forces added to this pressure and caused the oil and gas to flow upwards out of the buried basins. The oil and gas then migrated with the flowing saltwater in the permeable layers of material below the impervious layer serving as a cap rock until captured by anticlines, faults, stratigraphic traps, and other subsurface formations.
Along the coast of the Gulf of Mexico and other areas large bodies of salt penetrated the strata from far below the surface to create domes that could even be seen above the surface in many places. The actions of the salt left porous layers of rock turned upward against the impervious salt, formed pockets in the cap of the domes, and caused faults in the strata above or surrounding the domes to trap the migrating oil and gas. The origin of the salt has yet to be fully understood. Some believe that alone the Gulf Coast of the United States the salt may have originated from the thick horizontal layer of salt that starts on-shore near the northern Texas Coast and extends out for many miles below the waters of the Gulf of Mexico just off the Louisiana Coast. A similar origin is believed in other areas. Oil production on-shore along the Gulf Coast is often around the salt domes as well as many other formations. Similar oil and gas reservoirs are found universally.
In the early part of the industry, before the technological advancements in exploration and drilling that exist today, oil production was from wells drilled into shallow formations. Methane gas above and entrained in the oil maintained the underground pressure and displaced the oil up the wells to the surface. The gas in those earlier fields has long been taken off to provide fuel for homes and industry. Soon after came the installation of the familiar pumps (called “pump jacks”) towering above the ground with the cyclic movement of the giant rocking arms as they lift the oil to the surface. Water and steam pumped down into the oil-bearing formations under ground as a driving mechanism (water and steam flooding) has received a limited amount of success for extraction of additional oil from certain fields. Many of those fields are now mostly depleted of the oil considered to be recoverable. However, it is well understood by those in the industry that in most oilfields more oil remains in oil formations than the amount removed by the previous technology available, perhaps enough to greatly reduce the United States' dependency on foreign oil for some time in the future if production can be recovered. If a new method is successfully demonstrated, the production from existing fields could be almost immediate and at relatively low cost because the location of the fields are known, the formations from which the oil is produced is well understood, and many of the abandoned wells are already in place with minimum effort required for placing them back into production.
The method employed in this invention is to use inert gases produced by the combustion of methane or propane gases as a driving mechanism. The products of combustion are also generally referred to as “flue gases.” There have been a number of attempts to extend oil production in oilfields considered to be depleted of the readily recoverable oil by injection of inert gases into the oil bearing formations as a driving mechanism that have failed. A second problem experienced in the attempts at inert gas injection was the corrosive effects of flue gases on the equipment and piping both above and below ground. The present invention overcomes the deficiencies of previous methods and apparatus by removing the corrosive contaminants in the flue gases and controlling the direction of flow of the inert gases once injected into the underground formations. The key to the success of extending oil production by inert gas injection in a formation considered depleted of recoverable oil is the addition of a method of controlling the flow path or direction the gases have a tendency to take. The general approach over an entire production zone is to inject the inert gases into the lower level of the inclined oil sand (down dip) to drive the oil up the formations and prevent the gases from escaping by pumping water into the upper part of the oil sand (up dip) to drive the oil in a downward flow to intercept the oil being driven upward by the injected inert gases. The heavier water will block most of the gases from overrunning the oil and escaping out of the production zone.
Injecting the lighter gases through selected injection wells at the lower end of a formation and the heavier compatible water from selected wells in the upper end of that formation will increase the pressure in the formation between the injection points and drive the oil to selected production wells positioned between the two levels of injection to collect the oil and bring it to the surface. The compressible inert gases will maintain a higher formation pressure between the injection wells and keep the oil flowing to the production wells for a period of time after the gas injection is temporarily discontinued. In addition, apparatus designed to reduce costs of oil recovery have been incorporated into the oil production system including small and new crude oil production pumps to replace the large and expensive pump jacks currently used and make it economically feasible to produce even one-quarter barrel of oil per day from a well and a fuel gas generator to extract natural gas from the crude oil under production for operation of the internal combustion engines used to power compressors and electrical generators in the production field.
The inert gases are produced by powering a compressor with an internal combustion engine in the production field or obtained from the combustion flue of a nearby industry. Air is added to the combustion process, and as a result for one theoretical cubic foot (ft3) of methane fuel the volume of combustion products produced include 1 ft3 of carbon dioxide (CO2), 2 ft3 of water vapor (H2O), and 7.55 ft3 of nitrogen gas (N2). For propane fuel the volume of combustion products produced include 3 ft3 of CO2, 4 ft3 of H2O, and 18.87 ft3 of N2. The carbon dioxide and nitrogen gases constitute the inert gases obtained from the flue gases. In addition, nitrogen oxides are also produced and must be removed from the inert gases before injecting them into the underground formations to prevent extensive corrosion of the equipment. The exhaust gases are cooled and washed to remove the combustion water vapors and nitrogen oxides. The clean inert gases of carbon dioxide and nitrogen are then injected into the underground oil formations through existing wells. Following an initial period of injection required for gradually increasing the pressure in the formation, substantial oil either flows or is pumped out through adjacent wells or the injection of the inert gases is discontinued, and oil is allowed to flow back to the well into which the gases were injected when the huff and puff method is applied. The injection of gases into a well and production of oil from an adjacent well is referred to as the “flow through production” method of inert gas production. The injection of gases into a well to increase the pressure in the formation then allowing that pressure in the formation to force the oil to flow back to that same well is referred to as the “huff and puff,” or the “cyclic injection and production” method of inert gas production. In most instances, the specific method used is dependent on the viscosity of the oil being produced.
Saltwater brought to the surface with gas and oil from underground production wells is commonly referred to as “produced water.” The present invention relates to underground production formations where the natural gas has been nearly depleted; therefore, the produced water will be brought to the surface combined with some remaining gas and the oil. The produced oil and water are typically placed into large tanks (often referred to as “gun barrels” in the industry) and allowed to separate by gravity. Although the oil is transported to refineries, the produced water becomes a waste product. However, in the methods employed by the present invention the produced water becomes a valuable commodity to be filtered and injected into the same underground formation from which it originates to act as a blocking mechanism to prevent the injected gases from escaping and direct the flow of the gases driving the oil to the production wells.
Shallow oil producing formations frequently contain oils with higher viscosities than the deeper wells where the volatile products may not generally escape. The viscosity of heavy oils can be reduced by absorption of carbon dioxide (CO2). Where it is determined from laboratory analysis that the reduction of oil viscosity of the oil in the underground formations would be economically beneficial to the production process, carbon dioxide can be separated from the nitrogen gas to nearly 100 percent of the—injection gases to reduce the viscosity of heavy oils. The nitrogen gas can be released to the atmosphere, transported to other oilfields for injection, or used for injection in another part of the oil formation under production as a driving mechanism when the carbon dioxide gas has reduced the heavy oil viscosity. Membranes may be used to separate the nitrogen from the carbon dioxide in flue gases. The membranes are typically employed for production of nitrogen gas with air as the source of nitrogen. The membrane used are assemblies of many thousands of hollow polymeric fibers each approximately the size of a human hair with the inside surface treated to produce a thin film on the inside surface that actually becomes the membrane that allows oxygen molecules to flow through the membrane and reject the larger nitrogen molecules. The porous material below the membrane surface serves as a support. The membranes also allow other gases with molecules smaller than that of nitrogen to flow through and be separated from the nitrogen gas. The result is for pure nitrogen to be separated from all other gases, including water vapors, in atmospheric air. In applications other than oil production the nitrogen is collected and stored, with the gases other than nitrogen typically discharged to the atmosphere. For injection into a heavy oil formation the flue gases can be separated for concentration of carbon dioxide where it is beneficial and economically feasible to do so. The normally discarded gases that flow through the membranes become the product to be collected for injection into the underground heavy oil formation.
The boundaries of the productive formations in existing oil fields were defined in the development and planning phases following the discovery of oil in those areas. The location and spacing of wells on a particular formation was based on the specific structure of the formation and on the number of different operators on the field attempting to achieve maximum oil production. Regardless of how well spacing was originally determined, detailed records of what was accomplished were kept and can be used as a reference to establish a general approach to additional production in specific fields. The structure of the formations, the spacing and location of the wells, and the viscosity of the oil to be produced will determine which wells are selected for inert gas and water injection and the specific method of either flow-through production or cyclic injection and production (huff and puff) from each well.
With the natural gas nearly depleted over the oil in the underground formations where the oil production is to occur methane for engine fuel may not be readily available in the oilfields. The cost of a natural gas (methane) pipeline or the trucking of propane to some of the oilfields may be substantial. In those fields the fuel gas might be economically extracted from the crude oil produced in those oilfields by a fuel gas generator. The gas extracted from the crude oil can be used as fuel for the engines that power compressors, and for other engines that power generators to supply electrical power for pumps, cooling tower fans, controllers, and area lighting where electricity is not readily or economically available, or for competitive cost advantage over other methods of producing oil from nearly depleted formations.